1. Field of the Invention
This invention relates to a ripple reduction technique for reducing a ripple of an output of a multiphase power supply device which supplies power of low voltage and large current to a high-performance processor, for example.
2. Description of the Related Art
In recent years, various types of personal computers such as notebook-type personal computers and desktop-type personal computers are developed, sold and widely popularized. Further, the performance of the processor mounted on the personal computer is markedly enhanced and power supplied to the processor tends to have a lower voltage of 1 volt (V) and a larger current of 100 amperes (A), for example, as the performance is more enhanced.
In order to supply such power, recently, a so-called multiphase PWM (Pulse Width Modulation) control DC/DC converter power supply device having a plurality of PWM switching DC/DC converters connected in parallel is often used (refer to U.S. Pat. No. 4,195,333, for example). The PWM switching DC/DC converter is a DC/DC converter having a function of controlling the output power amount by changing the output (ON)/interruption (OFF) period in each cycle. The multiphase PWM control DC/DC converter power supply device generates power of desired low voltage and large current by controlling the switching operation of each PWM switching DC/DC converter.
The output current of the multiphase PWM control DC/DC converter power supply device which is generated by use of a plurality of PWM switching DC/DC converters generally becomes a ripple current containing a variation. Conventionally, it is possible to select the number of phases of the multiphase PWM control DC/DC converter power supply device and supply voltage to the multiphase PWM control DC/DC converter power supply device so as to suppress the variation in the ripple current to minimum. However, the output ripple current is greatly changed according to a variation in the supply voltage and a change in the output voltage (the supply voltage must be changed in some cases according to the consumption current in the recent processor). Therefore, the ripple voltage becomes high and there occurs a problem (associated with the cost and space) that the electrostatic capacitance of a so-called smoothing capacitor must be made large by taking the above case into consideration. Further, there occurs a problem of the performance that a power loss occurs when a large ripple current flows into the capacitor and the efficiency is lowered.
Further, the multiphase PWM control DC/DC converter power supply device is required to change the output voltage depending on a difference in a load to be connected. Also, at this time, the same problem as described above occurs, and if the output voltage must be changed to a greater extent, there occurs a problem that the above capacitor must be replaced by a capacitor with larger capacitance.